1. Field of the Invention
The present invention relates to a jack, and more particularly a power jack which incorporates stress components, and which is adapted to be advantageously, although not exclusively, employed in equipping the flight control system of the usual type of aerodyne, for example, an airplane or a helicopter.
In general, it is known that direct control over such aerodynes is achieved by the action of the pilot on at least one operating lever, such as a control or steering column which is connected to the control devices of the aerodyne through the intermediary of steering apparatus and shafts, as in the instance of a system for varying the twist or pitch of the rotor blades of a helicopter.
This direct control has an accessory back-up provided by an automatic pilot system, or automatic pilot, which acts on a jack allowing for rapid piloting, but which has a limited scope of operation.
Thus, in order to prevent this jack, which is associated with the automatic pilot, from acting on the operating lever, i.e., control column, instead of effectuating the command of the controls it is necessary to provide a device that acts upon the operating lever, and which will exercise a greater counteracting force above the jack of limited operating range, than that of the resistance below the jack which is exerted by the controls.
Within the basic technology such a device may include a tension spring or a compression spring, which will oppose the stress according to a predetermined principle, usually referred to as the "principle of stress," located above the jack, and in which the position of its mounting or anchorage can be varied, for example, by means of a jack, such as a power or stress jack.
This type of jack may include, in the basic technology, a motorized speed reducer, which can, on occasion, be controlled by the automatic pilot, or by the pilot himself, having an externally projecting shaft which responds to a lever (or mounting), on which the spring is articulated.
A shift of the anchoring point of the spring thus permits the position of the operating lever or control column to be readjusted, and the jack may be maintained in a position so as to have the greatest extent of travel (around a zero point), which is important because, as is well known, these jacks have a very limited degree of travel.
One of the advantages of this system, and, particularly when the stress principle is incorporated therein, is that it restores a sensation or feel to the hands of the pilot which allows him to recover a position corresponding to a particular flight pattern.
Finally, it is to be noted that these systems may include, on the one hand, a device for detecting a shift of the external shaft or axis with respect to the anchoring point, and which can, for example, be constituted of a micro contact breaker serving to stop or to minimize the action of the automatic pilot, for example, by blocking the jack, or by limiting its movement, which would otherwise conflict with the action of the pilot when he shifts the operating lever; and, on the other hand, a device for disengaging the anchorage, thus permitting the spring which utilizes the stress principle to be recentered.
2. Discussion of the Prior Art
Currently, all of these functions are performed by modular elements which are connected to each other by mechanical means and which are usually exposed to the open air. As a result, these elements are not reliable, they are difficult to adjust and control, and they age very poorly, particularly in a salty atmosphere. As a result, the life expectancy of such a system frequently barely exceeds fifty hours of service.
Furthermore, these prior art systems are all subject to a serious drawback in that, when the anchorage is disengaged, there occurs a recentering or shifting of the spring so as to cause a serious discontinuity in the operation of the flight control system. This discontinuity quite readily is the cause of dangerous breakdowns and accidents.